This invention relates to an interventional catheter comprising a catheter tube having two superposed layers of materials secured together and with mechanical properties differing from one another, a guidewire lumen in the catheter tube for the sliding fit of a guidewire, and a balloon with a distal end sealingly surrounding the catheter tube whereby the catheter tube has an inner layer forming the guidewire lumen and an outer layer forming an outer surface of the catheter tube.
Over the wire catheters have been widely used for interventions such as percutaneous transluminal cardiovascular angioplasty. A problem with these catheters is that the guidewire may clog into the guidewire lumen of the catheter, whereby the guidewire may follow the balloon upon withdrawal thereof after the inflation procedure thereby making it necessary to re-insert the guidewire into the treated area of the blood vessel for repositioning a balloon therein in case a second inflation is needed. A further problem is that the catheter has to achieve an acceptable compromise between the requirements of some stiffness to assure good pushability and some flexibility to assure kink resistance. In addition, the catheter has to permit safe attachment of the balloon to the catheter tube.
Monorail(copyright) technology, which provides for an entry of the guidewire distal of the balloon and an exit for the guidewire distal of the proximal end of the catheter tube, substantially reduces the risk of the guidewire clogging in the guidewire lumen because the length of frictional engagement between the guidewire and the guidewire lumen is strongly reduced. That is also of great help in the handling of balloon catheters for balloon exchange purposes. Though limited, the friction and clogging problem is, however, still existent.
Two layer catheter shafts have been developed. For example, the document WO 92/11893 describes an intra-aortic balloon apparatus comprising a hollow catheter in which is located an elongated member forming a central lumen extending out of the catheter at the distal end thereof. An aortic pumping balloon is positioned over the elongated member; the distal end of the balloon is bonded to a tip affixed to the distal end of the elongated member, and its proximal end is bonded to the distal end of the catheter. In order to achieve a balance of flexibility and remains and to avoid kinking, the elongated member is formed of an inner layer comprised of a soft elastomeric material to impart flexibility to the tubing and the outer layer is comprised of a hard plastic material to impart structural support to the elongated member. This balloon apparatus cannot be loaded with a guidewire and moved into tortuous vessels with the guidewire loaded inside the elongated member as the friction between guidewire and elongated member increases distinctively when the elongated member is shaped into curves. There would be therefore the risk that a spiral wound guidewire could be captured in the soft elastomeric plastic material of the inner layer of the elongated member. Although the outer layer of the elongated member that is coextruded onto the inner layer is formed of nylon, a material which is expected to be directly weldable to a wide variety of materials, this balloon apparatus cannot be introduced into narrow vessels or narrow stenoses, nor can it be passed through narrow punctures to enter the blood vessels. This is because of the relatively large profile of the folded balloon, due to the distal fixture of the balloon to the elongated member. The balloon is bonded to an intermediate tip element which in turn is bonded to the elongated member.
The document EP 0 650 740 A1 shows a catheter comprising a catheter tube having two superposed layers of materials secured in relation to one another and with mechanical properties differing from one another, a longitudinal lumen in the catheter tube for the sliding fit of a guidewire, and a balloon with a proximal end and a distal end, the distal end sealingly surrounding the catheter tube, whereby the catheter tube has an inner layer forming the longitudinal lumen and an outer layer forming the outer surface of the catheter tube. In this catheter, the inner layer is formed of a material with lower friction coefficient than the material forming the outer layer, whereby there is no more risk of having the guidewire clogging in the guidewire lumen of the catheter tube.
In terms of two layers catheter shafts, it has been observed that in practical use the adhesion of the two layers of material was not absolutely satisfactory. Although the coextrusion technology currently used for making such catheter shafts seems to involve close molecular interpenetration of the materials forming the superposed layers of the shaft, it has been possible to observe separation of the two layers, for example at the place of insertion of the shaft over the guidewire. Furthermore, tear test effected on such structures has shown that the two layers can separate under extreme conditions of stress on the shaft.
It is an object of this invention to propose an interventional balloon catheter avoiding the aforesaid drawbacks A further object of the invention is an interventional catheter structure which is versatile and which provides a fully controllable and easy to manufacture assembly. Still a further object of the invention is an interventional low profile balloon catheter that can be safely operated on a guidewire and moved into tortuous vessels and other extreme conditions.
Various multilayer catheters are known in the art. Reference is made to U.S. Pat. Nos. 4,627,844; 4,636,346; 5,403,292; 5,499,973; and 5,538,510.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.
Accordingly, where the catheter comprises mediator layer means arranged between the inner layer and the outer layer for the adhesive anchorage of the layers thereto, securing of the inner layer and outer layer is strongly enhanced independently of their intrinsic capacity of adhesion to one another. The risk of a poor adhesion or the risk of a failure in the adhesion of the two layers to one another is eliminated. The inner and outer layers may be chosen for their most appropriate mechanical characteristics rather than for their capacity to adhere to one another. Because of the adhesive anchorage of the inner and outer layers on the mediator layer means, the risk of separation of the two layers upon insertion of the catheter tube over a guidewire is minimized. And the assembly of inner and outer layers is under control and the possibilities of changing the flexibility of the assembly are improved; due to the adhesive anchorage on the mediator layer means, rigidity of the assembly is enhanced with the same basic inner and outer layers, whereas flexibility of the assembly may be mastered by safely acting on the thickness of the inner and outer layers, with the resulting reduction in the profile of the catheter. As a result of the adhesive anchorage of the inner and outer layers on the mediator layer means the assembly behaves like a unit; accordingly, the assembly may be safely grabbed by the outer layer and tear tests are thus facilitated.
The inner and outer layers and the mediator layer means may be congruent in length, so that the catheter shaft can be produced in long tubes which may be cut at will to the appropriate length. Where the inner layer, the mediator layer means and the outer layer are coextruded, a catheter tube is formed in a continuous process avoiding the need of using a core in the inner layer.
Where the inner and outer layers are substantially transparent and the mediator layer means are contrasted with respect to the substantially transparent inner and outer layers, a visual control of the assembly is readily available to further improve the manufacture.
Where the mediator layer means have mechanical properties differing from the mechanical properties of the inner and outer layers a further step is achieved in the possibility of changing the lengthwise flexibility properties of the catheter.
When the inner layer is formed of a material with lower friction coefficient than the material forming the outer layer, there is no more risk of having the guidewire clogging or being captured in the guidewire lumen of the catheter tube. Withdrawal and re-positioning of the balloon catheter on a guidewire left in place at the site of treatment in the vessel system is rapid, safe and precise. Furthermore, the choice can be made for materials for the inner and outer layers having the most appropriate friction and kink resistance coefficients, while safe attachment of the balloon may be made at will on the outer layer which is chosen without being influenced by the friction properties of the inner layer.
The mediator layer means may be formed on the basis of a low density polyethylene to offer superior adhesion performance in a wide variety of configurations of the inner and outer layers and ease of processing on conventional fabrication equipment.
In a preferred form of the invention, the inner layer is made of a polyethylene or of a high density polyethylene, both of which assure an extremely low friction coefficient and an appropriate kink resistance coefficient. In another preferred form of the invention, the outer layer is made of a polyamid to assure easy welding of the balloon and a good stiffness at that level.
In sum, the invention relates to an interventional catheter comprising a catheter tube having two superposed layers of materials secured together and with mechanical properties differing from one another. A guidewire lumen is formed in the catheter tube for the sliding fit of a guidewire, and a balloon with a distal end sealingly surrounding the catheter tube. The catheter tube has an inner layer forming the guidewire lumen and an outer layer forming an outer surface of the catheter tube wherein it comprises mediator layer means arranged between the inner layer and the outer layer for the adhesive anchorage of the layers thereto. The inner and outer layers and the mediator layer means may be congruent in length. The inner layer, the mediator layer means, and the outer layer may be coextruded. The inner and outer layers may be substantially transparent and the mediator layer means may be contrasted with respect to the substantially transparent inner and outer layers. The mediator layer means may have mechanical properties differing from mechanical properties of the inner and outer layers. The inner layer may be formed of a material with lower friction coefficient than the material forming the outer layer. The mediator layer means may be formed on the basis of a low density polyethylene. The inner layer may be made of a polyethylene. The inner layer may be made of a high density polyethylene. The outer layer may be made of a polyamid.
These and other objects, features and advantages of the invention will become readily apparent from the following description with reference to the accompanying drawings which show, diagrammatically and by way of example only, preferred but still illustrative embodiments of the invention.
As will be realized, the invention is capable of other and different embodiments and methods of construction, and its several details are capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.